This invention relates to an apparatus for automatically measuring the electrical characteristics such as carrier concentration, etc. of a semiconductor wafer.
In manufacturing a semiconductor device by using a semiconductor wafer, it is required to examine in advance its electric characteristics, such as conductivity, carrier mobility, and carrier concentration, etc. to make a wafer selection. If a judgment as to whether or not a wafer is bad is not made properly, a yield, reliability, and increased cost arise.
For examining the electric characteristic of a semiconductor wafer, there is an apparatus using the van der Pauw method which is a representative measurement method. With this device, however, since the formation of an ohmic electrode is required, the wafer must be destroyed.
In view of this, there is proposed an apparatus which does not require destruction of the wafer, as the device for measuring conductivity, carrier mobility, or carrier concentration (Japanese Patent Application Laid Open No. 136182/79).
In the case of such a conventional apparatus, however, the configuration of the detection system of the device becomes complicated and practical measurement accuracy cannot be provided. Since the optimum measurement condition of conductivity and carrier mobility are different from each other, it is difficult to satisfy both conditions at the same time. Further, because a strong magnetic field is required for measurement, the influence of the magnetic field may affect the measurement of conductivity.
However, in the case where the apparatus based on the van der Pauw method is used, it is impossible to measure the total number of wafers because of the destruction is stated above. It takes a long time for measurement, including the time required for preparing a sample. In addition, one is unable to make a detailed measurement of the distribution in the wafer plane. For this reason, it is impossible to examine whether or not the total number of wafers quarried from an ingot satisfy the carrier concentration standard, or to measure the sheet carrier concentration of an ion implanted layer by in-process. Accordingly, such an apparatus cannot contribute to management or control of the wafer quality or improvement in the wafer.